A number of resistance-type bicycle training devices have been developed that allow a person to stationarily train on a bicycle. Such bicycle training devices are commonly used indoors when it is not possible to ride the bicycle out of doors. Such bicycle training devices normally include a collapsible frame positionable on a floor and releasably attachable to the rear wheel of the bicycle. The frame supports a resistance unit which engages the rear wheel of the bicycle supported by the frame, to provide resistance to the rotation of the wheel. Therefore, as the person moves the pedals and, consequently, the rear wheel of the bicycle, the rotation of the wheel is opposed by the resistance provided by the resistance unit.
The resistance units utilized with devices of this type take many forms, including units utilizing fluid resistance mechanisms, electric resistance mechanisms and air resistance mechanisms, among others. While each of these types of resistance units provides adequate resistance to the rotation of the wheel in order to simulate outdoor riding, each type of mechanism also has certain drawbacks which limit the ability of the resistance unit to vary the simulated riding conditions.
As a result, many types of resistance devices now include magnetic resistance units which overcome many of the drawbacks associated with other types of resistance units. Certain types of magnetic resistance units normally apply resistance to the rotation of the bicycle wheel by application of eddy current forces to a conductive member which rotates along with a rotatable wheel or flywheel, which rotates along with the bicycle wheel. The eddy current forces result from rotation of the conductive member relative to a set of magnets positioned adjacent the conductive member. By moving the magnets relative to each other, an individual can adjust the flux density created by the magnets thereby the strength of the eddy current forces, to vary the resistance to the rotation of the flywheel. The resistance to the rotation of the flywheel is transmitted to the bicycle wheel, to vary the amount of effort on the part of the person to rotate the bicycle wheel in order to overcome the resistance provided by the magnets. A number of examples of bicycle trainers with magnetic resistance units which operate along these lines include Minoura U.S. Pat. Nos. Re 34,479; 5,468,201; 5,728,029; Lee U.S. Pat. No. 5,711,404; Hu U.S. Pat. No. 5,382,208; and Gunther et al U.S. Pat. No. 6,042,517. In each of these units, a number of magnets are disposed adjacent a conductive component interconnected with a flywheel a. As the flywheel rotates, the magnets establish eddy currents in the conductive member, to resist the rotation of the flywheel. The person can adjust the amount of resistance provided to the flywheel by utilizing a cable connected to an adjustment mechanism disposed within the resistance mechanism, that adjusts the position of the magnets with respect to each other or with respect to the conductive member, to increase or decrease the amount of resistance applied to the rotation of the flywheel.
While magnetic resistance units of this type are useful in providing a variable degree of resistance to a person utilizing a training device including the magnetic resistance unit, the structure of these units requires that the person must actively control the amount of resistance provided by the resistance unit at all times. Thus, if the person wishes to increase or decrease the amount of resistance supplied by the resistance unit while exercising, the person must manually adjust the position of the magnets in the resistance unit to achieve the desired amount of resistance. When exercising on the bicycle, it is highly inconvenient for a person to have to adjust the resistance provided by the resistance unit to achieve the desired level of resistance.
Therefore, it is desirable to develop a magnetic resistance unit for a bicycle trainer that has a simple construction and that automatically adjusts the resistance provided by the resistance unit. It is further desirable to have a magnetic resistance unit that provides progressive adjustment in the level of resistance according to the speed of rotation of the bicycle wheel.